1. Field of the Invention
The present invention relates to a device for generating a lossless pulse ultraviolet laser beam, and more particularly, to a device of generating an ultraviolet laser beam having a desired wavelength by allowing a laser beam generated using a pulse ytterbium fiber laser to pass through nonlinear harmonic crystals and then rotating the laser beam several times.
2. Description of the Related Art
A laser is the acronym of a “Light Amplification by Stimulated Emission of Radiation.” A laser beam is a pure powerful light with high collimation and monochromaticity which is amplified by stimulated emission of radiation.
A laser beam is widely used in several applications. For example, a powerful laser beam is used to mark, drill, cut, and weld steel plates, solid jewelry, plastics, etc. in industrial fields, and exhibits excellent effects in LASIK surgery, dental surgery, disk surgery, gynecology surgery, etc. that are most widely known in a medical field.
In a munitions industry, a laser beam is also widely used to remove land mines and monitor the invasion of an enemy. In communication fields, the laser beam is used to transmit much information more quickly.
Particularly, an ultraviolet (UV) laser beam has an oscillation wavelength of 15 to 400 nm.
When a laser beam having a wavelength of 200 nm or less passes through the air, it is substantially absorbed into the air just at a few centimeters of the air layer. Thus, the wavelength range of the laser beam is called an ultraviolet range because it can be used only in a vacuum environment.
The wavelengths of the laser beam enable different tasks to be performed.
For example, a laser beam having a wavelength of 355 nm is used for marking glass, drilling via holes, prototyping, and manufacturing a light mask and a compact mask for a liquid crystal display (LCD) device, a plasma display panel (PDP) device, etc., and a laser beam having a wavelength of 266 nm or 213 nm is used for semiconductor lithography, an extreme ultraviolet interferometer, a confocal microscope, a substitution of an excimer laser, etc.
The UV laser beam may also be used to measure air pollution.
For example, an UV laser beam irradiated by an artificial satellite and an UV laser received by a ground observatory are compared with each other in order to measure the air pollution.
This is because various factors causing air pollution absorb the UV laser beams. Representative air pollution factors include nitrogen dioxide (NO2) in a 450 nm wavelength, sulfurous acid gas (SO2) in a 300 nm wavelength, ozone (O3) in a 290 nm wavelength, etc.
Two conventional UV laser beam generating systems include an excimer laser system, and an Nd:YAG laser system in which a light emitted from an Nd:YAG laser is passed through a nonlinear harmonic crystal so that the wavelength of the light is converted.
The excimer laser system generates beams of several wavelengths including an XeF laser beam (oscillation wavelength: 351 nm), an XeCl laser beam (oscillation wavelength: 308 nm), a KrF laser beam (oscillation wavelength: 248 nm), a KrCl laser beam (oscillation wavelength: 222 nm), and an ArF laser beam (oscillation wavelength: 193 nm) by changing a medium for the excimer laser.
The Nd:YAG laser system obtains a desired wavelength by passing a laser beam having a 1064 nm wavelength oscillated in an Nd:YAG laser through a nonlinear harmonic crystal.
However, the excimer laser system requires different mediums to be used dependent on objects to be machined. In addition, a medium, poisonous gas, should be replaced, a laser mirror should be periodically cleaned and aligned, and system maintenance is costly.
The Nd:YAG laser system has a limitation in machining products because it emits the light beam of one constant wavelength of 1064 nm, and requires an appropriate nonlinear harmonic crystal for changing the wavelength of the laser beam.
In addition, the Nd:YAG laser system cannot obtain a desired wavelength when the crystal is positioned at an incorrect angle. Accordingly, the crystal should be aligned each time the crystal is periodically replaced. In addition, the laser mirror should be cleaned.
In addition to the inconveniences and high maintenance cost, such conventional UV laser exhibits low energy efficiency of about 2 to 3% and has poor beam quality.
Further, a great amount of an intermediately-processed or finally-output UV laser beam is lost when it is used in practice.
This is because laser beams having other wavelengths are emitted together with the UV laser beam even when only the UV laser beam is made to be emitted.